WASHINGTON — Many Republicans hail Fred Thompson as a candidate who brings an unmatched combination of conservatism and electability to the presidential race, but his stance on at least one key social issue — abortion — is similar to that espoused by Senator McCain and Mitt Romney, two of his top potential rivals.

While the former Tennessee senator opposes the Roe v. Wade decision and built a solidly anti-abortion record in Congress, he has indicated that he would not move to outlaw the procedure.

That position puts him roughly in line with Messrs. McCain and Romney, but for some hard-line abortion foes, it falls short. They say that even with Mr. Thompson in the race, many voters who oppose abortion rights may still view Senator Brownback of Kansas and a former Arkansas governor, Michael Huckabee, as the only acceptable choices. That could spell trouble for Mr. Thompson, whose viability may hinge on attracting supporters away from the top-tier contenders.

Mr. Thompson would enter a race in which social conservatives have yet to coalesce around any of the three leading candidates: Messrs. McCain and Romney and Mayor Giuliani, who has held more liberal views on social issues. Mr. McCain has consistently voted against abortion, but many conservatives are wary of him, while Mr. Romney’s position on several hot-button issues, including abortion, has shifted to the right only in recent years.

Mr. Thompson, who has formed a “testing the waters” committee and is likely to make an official announcement of his candidacy soon, has long taken a federalist approach to abortion, saying that Roe v. Wade should be overturned and that states should decide the issue for themselves. He opposes a constitutional amendment banning abortion, his spokesman, Mark Corallo, said yesterday.

Messrs. McCain and Romney have also advocated an overturning of the Roe decision, but not an outright federal ban.

In an interview on Fox News last week, Mr. Thompson said he “would not be and never have been for a law” that would criminalize a woman.
Abortion opponents said that is a commonly held political stance and that most proposals to ban abortion would focus punishment on the provider, not the woman.

But Mr. Thompson’s assertion of states’ rights on the issue does not satisfy some in the anti-abortion camp. “It wouldn’t be an acceptable answer,” the head of the Pro-life Action League, Joseph Scheidler, said.

Mr. Scheidler said his group advocates federal legislation to prohibit abortion and for the law to treat the unborn as equal to children who have been born. “We’re going for broke on this,” he said. For that reason, he said, some anti-abortion voters may look to a candidate like Mr. Brownback, whom he described as “about as right as you can get” on abortion.

The Kansas senator has run largely on a socially conservative platform, and he has said the Republican Party should not nominate a candidate like Mayor Giuliani, who supports abortion rights. In a brief interview yesterday, he tried to set himself apart from Mr. Thompson.

“He hasn’t led on these issues,” Mr. Brownback said, referring primarily to abortion and embryonic stem-cell research. “He’s a fine man, but these are priorities for me. Because I think it’s the central issue of our day — whether we’ll stand for life.”

During his race for the Senate in 1994, Mr. Thompson was quoted as saying that the abortion decision “should be up to the woman,” and he has indicated on a questionnaire that abortion should be legal during the first trimester.

His supporters quickly point to endorsements in his two races by the National Right to Life Committee, along with his legislative record over eight years, during which he earned a 100% rating from the group.

The legislative director for the committee, Darla St. Martin, said Mr. Thompson had “an excellent pro-life record” and that the organization did not have a problem with his statement last week on Fox News. “I think he and his people realize that we know what his position is,” she said.

Some abortion opponents see Mr. Thompson as solid in the two areas where a president can have the most influence: He opposes federal funding and supports “strict constructionist” judges. “I don’t see them presenting any problems for the pro-life movement in terms of the powers the president has to exercise,” the vice president and executive director of Americans United for Life, Daniel McConchie, said.

There has also been speculation about whether Mr. Thompson’s personal history and ties to Hollywood will be an issue for social conservatives. The “Law & Order” star is, like Messrs. McCain and Giuliani, divorced. His first marriage ended in 1985, and in 2002, he wed Jeri Kehn, a Republican strategist 24 years younger than he is.

Divorce is not necessarily a problem, a leading advocate for the Southern Baptist Convention, Richard Land, said. “Almost every evangelical voter has been touched by divorced,” he said. “What matters most is the number of divorces and the circumstances of the divorce,” he added, referring to the fact that Mr. Giuliani has been divorced twice, the second of which included charges of infidelity.